Liquid pigment dispersions are widely used in formulating pigmented exterior colored solventborne paints for automobiles and trucks. The finish of choice currently being used on automobiles and trucks is a clear coat/color coat finish in which a clear coating is applied over the pigmented colorcoat or basecoat to provide protection to the colorcoat and improve the appearance of the overall finish particularly gloss and distinctness of image. It is well known that pigments used need to be ground to small particle size and dispersed in a liquid for use in paints. Finely ground pigment, necessary for color and appearance, has a tendency to clump together resulting in paints with poor color development and non-uniform appearance. It is also well known that the rheology of such pigment dispersions has a dramatic effect on the paint spray viscosity and final appearance of the paint film. One major concern is that if rheology is not maintained at proper levels, the desired paint appearance is not attained.
This is a well known problem. Attempts to solve this problem in the past have included the use of polymeric pigment dispersants, especially polymeric dispersants containing quaternary ammonium groups, to stabilize the finely ground pigment particles. Generally such systems successfully stabilize particles but proper rheology control has not been uniformly attained. Another solution that others have previously adopted is to lower the pigment loadings in the paint. While the spray viscosity can be maintained at desired levels using this approach, this technique leads to paints with lower hiding power that require spray application at higher film builds to achieve the desired color and effect, which is time-consuming and expensive.
Accordingly, there is still a need to provide pigment dispersions wherein the dispersion rheology can be maintained at the desired levels throughout the shelf life of the paint.